Automatic firearm of the blow back type



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Dec. 17, 1957 Flled Aug 27 1951 Dec. 17, 1957 R. R. GRAGEs 2,816,484

AUTOMATIC FIREARM oF THE BLow BACK TYPE Filed Aug. 27,. 1951 4 Sheets-Sheet 2 /A/f/z/fa/T RICHARD R. GRAeEs Deal?, 1957 R. R. GRAGl-:s

AUTOMATIC FIREARM oF THE BLOW BACK TYPE Filed Aug. 27. 1951 l 4 Sheets-Sheet 3 a a. m @9L w www m @QS wrm/fm RICHARD R. GRAGES Dec. 17, 1957 R. R. GRAGEs 2,816,484 y AUTOMATIC FTREARM oF THE BLow BACK TYPE Filed Aug. 27, 1951 4 Sheets-Sheet 4 l A l f ya I T l?? I T FIG. 23.

Patented Dec. 17, 1957 AUTOMATIC FIREARW F THE BLOW BACK TYPE Richard R. Grages, St. Louis, Mo.

Application August 27, 1951, Serial No. 243,801

2 Claims. (Cl. SSL- 194) This invention relates to automatic rifles, and more particularly to those of portable, automatic and semiautomatic character, and those sometimes referred to as sub-machine guns. The present invention as depicted in the improvements presently disclosed, further relates particularly to automatic arms of the general type sometimes designated as designed for blow back actuation, as distinguished from those in which the cyclic operation of the gun is edected by direct recoil, and those of types in which operation is derived from the energy of gases under pressure trapped in or near the muzzle region of the rifle barrel.

This designer is aware of many earlier attempts to achieve a lightweight, simple arm of the general type designated and which will be relatively inexpensive in manufacture, sturdy, dependable and service-free in operation and which requires little or no skill incident to its assembly and disassembly, as for cleaning and maintenance. So far as is reterminable at this writing, all small caliber guns of this type fall far short of realizing these recognized objects, the attainment of which constitutes a major and general object of the present improvenients.

Perhaps the primary object of the present invention may be stated as realized in an extreme simplification of the gun and its working parts; this object is realized in the present embodiment in an arm which, apart from firing control mechanism, need involve no major working elements other than a bolt and firing pin assembly and a spring therefor, together with the usual minor accessory features such as magazine, extractor, ejector and the like.

Yet another highly important objective of the present improvements is realized in a virtually recoil-less gun of such character as to exhibit important advantages in ability to be held on the target, and to possess an irnproved general firing accuracy, whether employed in full automatic or semi-automatic operation.

A still further and highly valuable objective is realized in correlation with the simplification heretofore referred to, and which objectively realizes a structure in which, upon removal of a single closure of the bolt-passageforming structure, enables dumping of the few major operative parts of the gun, by gravity, for disassembly, with reassembly of same in a reverse order, all without requirement of special tools or skill.

A still further and highly valuable objective of the present improvements is realized in a generally improved and highly efficacious air-cooling arrangement such that, incident to the firing of each round, there directly results, partly by an induced ow of air, a cooling stream which sweeps and clears of burnt gases the space in the receiver forwardly of the bolt, at the same time resulting in a stream of cooling and scavenging air forwardly along the barrel. As an adjunct of the cooling structure, due

to special bolt formation and side openings in the receiver, there is provided an air ow along the bolt and to the rear of same from the rearmost end of the receiver.

Yet an additional and highly important object of the present improvements is realized in a more positive and powerful iow back actuation of the bolt and firing pin,

realized by a novel arrangement of gas passages in and along the bolt, together with gas piston formations on the pin, so coacting with the bolt passages as to insure a more positive cycling operation of the gun by gas re* action in the special piston formations.

The foregoing and numerous other objects will clearly appear from the following detailed description of a presently preferred embodiment which, for purposes of illustration but without limitation, is directed to a portable rifle of 9 mm. caliber; the full structure thereof appearing from a consideration of the description in conjunction with the accompanying drawing in which:

Fig. l is a side elevational view of an automatic rifle embodying the present improvements;

Fig. 2 is a top elevational view, or plan, of the rifle shown by Fig. l;

Fig. 3 is an enlarged fragmentary sectional view taken in a vertical plane through the barrel and barrel jacket, and including a portion of a receiver, Fig. 3 being taken along line 3-3 of Fig. 2;

Fig. 4 is a transverse sectional view taken along line 4-4 of Fig. 3;

Fig. 5 is a fragmentary sectional view in a horizontal plane as located by line 5-5 of Fig. 4;

Fig. 6 is a transverse cross sectional View taken in the muzzle region of the barrel and jacket assembly, and along staggered planes as identicated by line 6 6 of Fig. 3;

Fig. 7 is an end elevational view of the muzzle end of the gun, the location of this view being indicated by line 7-7 of Fig. 3;

Fig. 8 is a fragmentary sectional elevation taken along line 8 8 of Fig. 3;

Fig 9 is an enlarged fragmentary longitudinal sectional View through the receiver, showing the bolt therein in elevation, and showing certain parts of the manual ring control in elevation;

Fig. 10 is a horizontal sectional view taken longitudinally of the bolt and surrounding portions of the receiver, particularly along line lil-10 of Fig. 9;

Fig. 11 is a fragmentary cross sectional view taken along line 11-11 of Fig. 9, and showing the forwardl end face of the bolt in elevation;

Fig 12 is a side elevational View of the actuator or bolt With the firing pin removed therefrom;

Fig. 13 is an elevational view of the read end of the bolt, with tiring pin removed;

Fig. 14 is a bottom plan view of the bolt assembly from which is omitted the firing pin;

Fig. 15 is a cross sectional View through the bolt from which the pin has been removed, and is located by line 15--15 of Fig. 12;

Fig. 16 is a cross sectional view through the bolt, without the tiring pin, particularly as viewed along line 16-16 of Fig. 12;

Fig. 17 is a fragmentary cross sectional view showing portions of the bolt, one of the sear elements and adjacent parts, and is particularly located by line 117-17 of Fig. 9;

Fig. 18 is a fragmentary horizontal sectional view through a portion of the manual tiring control mechanism and adjacent parts, and is particularly located by line ILS- 18 of Fig. 9;

Fig. 19 is a fragmentary vertical sectional view showing portions of the firing control means, and is particularly located by line 1.9-1.9 of Fig. 9;

Fig. 2O is a fragmentary sectional view with parts in elevation taken through `the manual firing control mechanism, but showing alternate positions of certain of said elements, in comparison with the positions of the same parts as shown by Fig. 9;

Fig. 2l is a view similar to Fig. 20, except showing modified positions of certain ofthe tiring control elements;

Fig. 22 is a cross sectional view through the rear end f the receiver and closure cap therefor, with adjacent parts, and is particularly located by line 22-22 of Fig. 9, and

Fig. 23 is a fragmentary sectional view with certain parts in elevation, and is indicated as to location by line 23-23 of Fig. 9.

Referring now by characters of reference to the drawing, and first to Figs. l, 2 and 9, a tubular receiver 25 is integral with and a continuation of a breech housing Ztll and cooling jacket 200, the latter elements being described in greater detail subsequently. The elongate tube structure is detachably secured to the stock, and seats in an arcuate channel 159 provided on the horizontal stock member shown as extension 158, sometimes referred to as a forearm. To the rear of the breech housing, the tube is formed interiorly to provide a smooth cylindrical passage for reciprocal actuation of the actuator, generally indicated at 26, and for convenience, usually hereinafter referred to as a bolt. The simple construction and arrangement of the actuator, the tiring pin 27, and recoil spring permits efcient operation, and affords quick and easy disassembly for cleaning, and provides equally for rapid reassembly.

A cap element 31 constitutes a closure at the rear of the receiver, and is provided with internal mutilated threads 32 (Fig. 22), which engage corresponding mutilated threads provided on the end of the receiver 25. This is la preferred construction, since there is required only a fractional part of a turn for complete detachment, facilirtating assembly and disassembly. From Fig. 9, showing the closure cap 31 and tube assembled and seated on the stock, it is apparent that the cap is provided with a central aperture 33, and another smaller aperture 34 directly thereabove. These openings serve as passageways for a pair of plugs or studs extending forwardly of a detachable rear securement member 36.

The slidable catch element positioned by the cap 3l, consists of two parts connected by the intervening studs, one part 35 located internally of the receiver, and the other designated at 36, located externally of the cap. rl`he former part comprises a circular plate 37 contiguous with the inner cap face, a peripheral inturned flange or collar 4t), and a relatively large center boss 41 of circular crosssection, the rear portion of the recoil or bolt-spring 36 being positioned about the boss with the end turn 42 bearing against the face of plate 37. The studs formed integrally with the plate, extend through the cap and secure the slidable external catch portion 36. A lower projecting flange 43 presents an upturned planar surface 44.-, that normally underlies a coacting flange 45 of the cooperating securement element, to lock the tubular structure in accurate position and alignment. A curvilinear surface 46, provided on the slidable catch above the flange and opposite the smaller stud, provides a thumb in moving the catch against the loading of spring 30 for disengagement of the normally overlapping grip flanges 43 and 45, incident to disassembly. The stationary and cooperating catch member comprises a bracket plate t7 and a downturned right angular flange Si) seated in a conforming recess formed in the upper stock surface, adjacent the arcurate channel, and secured thereto by a screw Sl passed through the upwardly extending boss portion 52.

On the right hand side of the receiver 25, as viewed in Figs. l and 2, is an elongate slot 53, extending longitudinally along the tubular structure. This slot coacts with thelalterally projected finger piece S4 constituting a bolt lever or handle, rigidly attached to the actuator or bolt 26, through which the bolt is prevented from rotation, but is guided in a straight line for reciprocal movement. A short safety slot is provided slightly above and as a branch continuation of the rear portion of the elongate slot 53, and is reversed forwardly to form the small leverbearing safety flange 56. Another shorter elongate slot 57 extends rearwardly yfrom the apertured safety region, and is disposed in a horizontal plane, which is slightly 4 t below the plane of the longer forwardly collocated slot. The function of the rear slot is merely to enable removal and re-assembly of the actuator from the rear of the tube, the slot being, of course, open in the rear when the cap 31 is removed.

The two land only major moving elements of the gun firing mechanism, are the actuator or bolt 26, shown by Figs. 9 through 16, and the tiring pin member 27 which is shown in assembly in Fig. 10. There are no other major moving parts, except of course, the operative compression-type spring 30, serving by preference as a combined bolt and pin spring.

The bolt which is indicated generally at 26, is a partly hollow, plug-like member of a generally cylindrical form serving several purposes, chiefly those of a loading member, a breech lock, ammunition guide, tiring pin retainer, support and guide, gas chamber, gas valve, gun locking mechanism, and safety lock. Also in coaction with the tiring pin member, considered as a piston, the bolt serves as a cylinder. It is to be especially noted that the bolt performs all of the usual purposes of a bolt, besides the other functions named.

Fig. ll is an end face view of the breech end of the bolt, showing a circular countersunk area 66 which receives the rimless cartridge head, and positions the round in the barrel chamber. An ejector claw 61 (Fig. l0), lying in a horizontal axial plane of the bolt, engages the usual groove adjacent the head -of the round, holding the round in place during ring, and in fact until the shell is ejected by an ejector flange 223, later described, the flange being located on the left hand side of the breech housing, just to the rear of a clip-receiving aperture 224, later referred to. The claw 61 is formed on the free end of the ejector, which is continued rearwardly of the bolt in a heavy spring shank 62, and supported at the opposite end by a plug 63 set into a socket 64 formed in the bolt, the spring shank 62 being able to ex in a longitudinal groove 65 in the bolt.

Directly opposite the ejector claw 61 is a longitudinal rib 66 (Figs. l2 and l5), provided with a guide slot 67, which slidingly engages the hooked ejector ange 223. The hooked flange, besides accurately guiding and directing the -bolt 26 in its forwardmost position, kicks the round from engagement with the claw upon return actuation of the bolt, expelling the empty casing through the ejection opening 222. A pair of relatively wide, deeply grooved gas passages 70 and 71 are provided adjacent the rib 66, and extend longitudinally along the bolt. r'he forward ends of these channeled passageways open into the front face of the bolt breech, and the rear ends open into Ia relatively large depthwise or radial gas entrance passages 72, thus directing the gas upon certain ring pin piston surfaces, the structure and function of which are later ful-ly described. One of the large grooves 71 provides an entrance 73 to a concave recess 74 serving as a gas reservoir and shown by the bottom plan view of Fig. 14. The recess '74 leads into an exterior longitudinal channel 75, and connects to a rear recess 76 by a narrow intervening slot '77. A pointed concave depression 80 formed in the annular collar portion 81 of the bol-t, provides a transverse shoulder 82 along the rear end, for locking engagement with the main sear 184 of the manual tiring control means exemplied by the illustrated trigger mechanism. The bolt handle or lever 54 is secured `to the side of the rear collar of the bolt by the integral stu-d 83, the latter snugly interfitting socket S4.

The tiring pin element 27 seats substantially within a correspondingly shaped axial bore or passageway formed through the bolt 26. The construction and configuration provides an elongate tubular piston-like portion 85, of circular cross-section, which aids in guiding and centering the pin in the bolt. An integral frusto-conical head formation 86 is located at the forward end of 85, the side walls 87 thereof being disposed at an angle converging toward the longitudinal axis, and thus, as will appear, forming a piston portion on the pin. The smaller end portion continues as an integral solid portion 90, and is so arranged when the pin is assembled with the bolt (Fig. l0), that the length thereof corresponds substantially to the diameter of the large radial gas passage 72. Another integral frus-to-conical portion 91 is shown adjacent to the portion 91), converging sharply to continue as a slender pin shank portion 92. This latter is attenuated at its frontal end to provide still another frusto-conical portion 93, which converges to the. striking end 94. When the firing pin is fully forward in` the bolt, the end 94 extends into the countersunk recess 60 of the front bol-t face, and a collar 95 provided approximately medially on the larger tubular portion 85, abuts the rear shouldered face 95 of the bolt and thus limits forward movement of the pin in the bolt. Fig. 9 clearly `shows that the portion of the tubular structure of the pin extending rearwardly of the collar, serves as a positioning boss -or spring plug 97 for the recoil or bolt spring, the spring encompassing the boss and abutting the rear face 16d of the collar 95.

There are three separate and distinct gas-directing channels provided in and on the actuator or bolt 26, which permit the gas to strike directly against pist-on formations on the tiring pin element 27 after discharge of the gun, the firing pin and the following actuator `being returned under spring loading, to the operative firing position. A quantity of the gas blown back into the bolt will enter through the pin opening in the center of the circular recess 6i) (Fig. 10), and will follow the pin rearwardly so that this supply of gas under pressure will be brought to impinge upon and react against the surfaces 87, 91 and 93, predominantly against the portion 91 as a piston, for rearward actuation of the ring element. Of course, it is obvious that there is sumcient clearance between the shank portion 9.?. and its enclosing bolt bore, to permit free passage of the gas.

A second gas-conducting path is provided in that the gas will pass along the deep-cut longitudinal `channels 70 and 71, and through the large radial passage 72, thence directly into reacting contact with the 4surfaces of piston or head formations S7 and 91, primarily against the former.

A third gas-directing channel is best viewed in Fig. 14, and is located externally along the bolt, the gas entering the groove 71, thence proceeding over the outer ridge 73 into the concave recess 74, thence into the longitudinal groove 75, this stream continuing through the slot 77, and thence outwardly through the rear recess 76 and into reactive impingement with the firing pin collar 95, from which it will now appear that collar 95 serves importantly as a gas piston.

However, because -of the prodigious gas pressures existing immediately `after firing of the round, auxiliary gas escape passages are provided in the bolt. A pair of small radial passages, which alleviate the pressure, are indicated at 101 and 162 in Fig. 16, and are arranged in right angular relation to the large gas passage 72 and ejector spring socket 64. There is another escape passage 233 provided in the breech housing, and described subsequently, and which assists in reducing the pressure in addition to producing other distinctly advantageous results, as will appear.

The stock 155 may be yof the usual construction and shown by Figs. 1 and 9 as consisting of a thickened shoulder piece 156, a relatively slender, curvilinear hand grip 157, and a rounded horizontal gripping element or forearm 15S. In assembly, the tubular receiver is seated and secured in an arcuate channel 159 formed in the upper surface of the horizontal element 15S. An angled lbracket member or hinge arm 161) is seated in a conforming recess in the upper forepart of the grip element 158, this bracket having an outward-ly projecting flange 161, and an arcuate bearing surface 152 (Fig. 1l) lying ush with the channel 159 for positioning the receiver. The ange 161 is apertured and secured by a bolt 163 to a companion flange 164 formed from the underside of the overlying extensa tubular clip` structure 165. A bolt 166. passed through the rounded' grip 158 is threadedly received by the member 160, thereby securing together the grip element and receiver as a unit.

The trigger control mechanism is contained in a case structure 167 depending from the lower side of the receiver, into a conforming slotted recess in the horizontal stock or forearm element 158, and is secured by screws 171B located through the side anges 171 and threadedly engaging the receiver (Figs. 17 and 21). The depending case 167 i-s further secured within the stock element and completely enclosed, by -a trigger guard 172 and its elongate, narrow anges 173, which are fixed by screws 174 directly to the stock.

Of course, the ring control means identied with the trigger mechanism, shown in Figs. 9, 18, 19, 20 and 21, will permit, selectively, either semi-automatic or full automatic tiring action, determinable by the position of a slidable push plunger, generally designated as 175, the structure and operation thereof being later described in greater detail. The drawing shows the plunger as being in semi-automatic firing position; however, it is obvious that if the plunger -were pushed to the opposite extreme, full automatic operation would be attained.

The provisions for automatic operation consist of a trigger 176 pivotally connected to the trigger guard 172, and having a small ringer projection 177 which normally bears against the hooked end portion 178 of lever 179. A compression spring 180 connected to the rear of the trigger, tends to urge the trigger to the inoperative position shown by Figs. 9 and 20, among others. The hook lever 179 is pivotally secured to one end of a slide element 181, the slide being journalled at its opposite end by a recess in an internal boss 182. Another spring 183 under compression, shown in Figs. 18 and 21, is located and secured to the lever 179 above the pivot, urging the lever downwardly for engagement with the trigger. The main sear 184 is pivoted at 185, and projects upwardly into the tubular receiver 25 for selective operative engagement with, and at times for retention of the bolt. A slot 186 in the slide 181 receives the lower end 137 of the Sear, and causes angular displacew ment of the sear about its pivot upon movement of the slide incident to firing actuation of the mechanism. Still another compression spring 138 tends to urge the sear 18a into retaining engagement with the bolt 26.

From Figs. 9 and 20 and the foregoing description, the automatic operation will be apparent, but for completeness and further clarity, it should be noted that, if the trigger 176 were pressed, the finger projection 177 would bear against the hook lever 179, moving the lever and attached slide 181 to the right. As the slide is shifted, the sear 184 is actuated in a counterclockwise direction, releasing the bolt for continuous firing operation. The gun will tire until the ammunition is exhausted, or the trigger is released, whereupon the spring 13S will urge the slide and lever to the left, and will urge the sear back to a position for operative retention of the bolt.

A camming sear 190 extends into the receiver, and cams against a longitudinal groove 75 on the underside of the bolt structure (Figs. 12 and 14). This sear includes an integral elongate lever arm 192 pivoted approximately midway in the casing 167. The opposite end of the lever arm is provided with opposed ears or lugs 193, which pivotally engage a smaller lever member 194, the latter lever having a small inturned ange 195 normally underlying the shank of the hook lever. A spring 196 secured to the lever, urges the flange under the shank.

For semi-automatic operation, the control mechanism operates to release the bolt in the same manner as for automatic tiring, viz., the trigger 176 is pressed, the hook lever 179 and connected slide 181 are shifted to the right (Figs. 18 and 20), pivoting the main Sear 184 counterclockwise (Fig. 20), hence releasing the springactuated holt 26. As the bolt is propelled forwardly,

the cam sear 190 bears against the camming groove 75 provided on the bolt, and is forced downwardly in the recessed portion provided in the horizontal stock member. The opposite end of the elongate lever 192 is moved upwardly, carrying therewith the small pivoted lever 194.1 with its integral projecting flange 195. This flange lifts the hook lever, until' the hooked end portion 178 rises above and clears the nose projection 177 on the tail of the trigger. Thereafter, the combined effect of the com pression springs urge the hook lever andl slide to the left, and the main sear in a clockwise direction (Fig. 2G) for operative re-engagement with the bolt upon return actuation thereof after firing. To fire a subsequent round, it is necessary to release the trigger, allowing the hook end of the lever to fall back for contact with the trigger nose projection, and again press the trigger, thus providing7 a positively controlled semi-automatic operation.

As is shown in Figs. 18 and 19, the plunger 175 provided for selection between automatic and semi-automatic firing control, is located immediately below the fiange 195 underlying the hook lever 179, and extends transversely through suitable apertures in the trigger guard and horizontal stock element, to opposite sides thereof. A slotted portion 197 provided approximately midway of the plunger, carries the flange in and out of operative position with the shank of the hook lever. Of course, the depressions 198 in opposite sides of the stock element, surrounding the push rod ends, facilitate selective manual actuation thereof, and provide protective shields minimizing accidental plunger movement. Another advantage is realized by including a camming surface 199 adjacent the slotted region 197, which moves the flange upwardly to seat on the top surface of the plunger, when the latter is shifted to the extreme left (Fig. 19) or automatic firing position. The camming sear 196 is lowered thereby from sliding contact with the bolt bearing groove 75, thus eliminating to a large extent any unnecessary wearing effect on the bolt and sear.

A cooling jacket Zlil is by preference formed integrally with and as a continuation of the receiver structure and breech housing 201, all being of circular cross-sectional shape, and in assembly the jacket is spaced outwardly from but arranged coaxially with the gun barr-el proper 2132. To facilitate the circulation of cooling air about and along the barrel, a plurality of circular apertures 283 are provided forwardly of the breech housing, and arranged in regularly spaced relation in longitudinal rows about the periphery of the jacket. Each alternate row is staggered, so that the apertures of adjacent rows will lie opposite the intervening metal webs, thus resulting in a defined pattern of air openings about and along the jacket.

Of course, any of the various popular and practical sighting devices may be used with this particular type gun, but the adjustable open sight shown by Figs. 1 and 2 is preferred for general usage, and is described chiefly for completeness. The front sight element consists of a planar, horizontal hase plate 204 that seats in and is secured to a conforming transverse slot 205 formed in the upper forward end surface of the cooling jacket, and an intervening, upwardly projecting sight tlange 266, which lies in a vertical plane containing the longitudinal axis of the tubular structure. The cooperating rear sight consists of a base bracket 207, a lever member 2% pivotally connected thereto, and an overlying slide element 2f-G9 adapted for angular adjustment of the lever, the structure being secured to the top of the receiver, with the sight notch in accurate alignment with the front sight flange.

In addition, the apertured jacket 200 serves as an anchorage for a hinged sling eye element, shown in Figs. 3 and 8, comprising an internal flat plate 210, a projecting arm 211 extending downwardly from the underside of the jacket, and a closed wire loop or eye 212 pivotally connected to the arm by a threaded bolt 213. A sling (not shown) such as ay strap, maybe extended through the loop or eye, and detachably connected to an eye member 214 secured to the stock.

Although the barrel proper 202 is shown by Figs. 1, 2 and 3 as of a relatively short or carbine length, the barrel length may be selected in accordance with the particular type and eld of usage of the gun. The barrel is provided with a precisely formed rifled bore 215 having uniformly spaced helical rifles or grooves, which formation comprises the lands 216 and intervening rifling 217 illustrated in Fig. 6.

In assembly, the integral, innermost hanged portion 220 of the barrel forms the forward wall of the breech housing 201, at the forward end of the receiver. The plate or block portion 220, being substantially of circular crosssection, tits tightly within the tubular receiver structure. The plate or block 220, in the breech region, is provided with a cartridge chamber 221 that extends directly into the barrel bore. A substantially rectangular opening 222 (Fig. 5) is provided in the right hand side of the breech housing, serving as an ejector opening through which the empty case is expelled after discharge. The breech housing also contains a guide rib or flange 223 secured rearwardly of a clip-receiving aperture 224 shown in the left hand side of the housing, which rib engages the guide slot 67 in the longitudinal rib 66 of the bolt.

The preferred construction of the ammunition feeding mechanism is shown in Fig. 2, although others may be adapted with only slight modifications of the breech, and consists of a sleeve structure secured about and contiguous with the breech housing 201. On the left hand side of the gun, as best viewed in Fig. 2, a rectangular tubular formation 225 is provided for the reception and detachable retention of a cartridge clip 226. A clamping screw 227 passed through a flanged portion formed rearwardly of the tubular clip receiving element 225, and another such screw member 163 through the bracket flange 161 on the underside of the gun, secure the structure about the housing and to the stock. A slotted region 230 in register with the ejector opening 222 in the breech housing, is provided in the sleeve structure to afford clear passage for the expulsion of the discharged shell casing. The cartridge clip 226 is of the spring-actuated type, which through a pressure plate, feeds the rounds successively into the breech housing incident to bolt actuation. It is particularly advantageous that the clip-receiving tube 225 and ammunition clip 226 be disposed in a horizontal plane relative to the normal operative tiring position, since the user will be afforded maximum protection when the weapon is red over a parapet or the like.

As is shown in Figs. 4 and 5, a concave or dished formation 231 is provided in the rear face of the wall element 220, converging and deepening toward the cartridge chamber 221. The coniguration and location of the dished formation facilitate quick and accurate positioning of each round, guiding and directing the nose thereof into the chamber, upon forward actuation of the bolt incident to tiring. On the opposite side of the chamber, a substantially rectangular relieved or sunken area 232 is formed in the inner face of member 220, which recess accommodates the ejector claw when the bolt is brought to its forwardmost position, the claw element engaging the annular rim recess of the round and holding it in place within the chamber, just prior to and during firing.

Several auxiliary gas escape passages are provided to relieve the tremendous gas pressure created within the breech housing immediately after firing. Among these latter escape ducts is the forwardly-directed gas passage 233, originating from the outer end portion of the relieved area 232, which serves not only to reduce the gas pressure, but in combination with the cooling jacket 209 and a vented end plug, plate or block 234, is instrumental in producing an improved cooling air ow. The conguration of the passageway 233 is such that the wider peripheral portion 235 thereof will upon insertion of the barrel into the jacket, clear the base plate 204 of the front sight member, and such that the smaller inner portion 236 will pass over the sling anchorage 210, when the barrel and the integral breech plate portion are inserted into or withdrawn from the cooling jacket, incident to assembly or disassembly respectively.

The vented end plug 234 is integral with and comprises an enlarged plate or block in the muzzle region of the barrel proper 292, and is of circular cross-section, having a diameter conforming to the internal diameter of the cooling jacket 209. The peripheral margin 237 of the plug is threaded to tit the corresponding threaded end portion of the jacket, thus providing a jacket-barrel bridging piece, and a flush gun end surface, as shown in Figs. 3 and 7. A set screw is threadedly received by the upper flange portion of the plug, the head 241 of the screw interitting a plug recess area and a curvilinear groove formation 242 in the internal surface of the jacket, hence locking the barrel proper and elements 220 and 234 in precise position and alignment. A plurality of regularly spaced vent apertures 243 are angularly spaced about the peripheral plug flange or block 234 which, in providing air passages along the barrel, cooperate with the circulatory features of the jacket and breech plate 22@ in producing improved cooling effects.

The barrel cooling characteristics of the gun are greatly improved by the deiinite forwardly-directed current of cooling air about the barrel proper 202. The gas pressure created in the breech region incident to tiring of the weapon forces a part of the gas through the escape passage 233 in the front breech wall element 220, causing a movement of air along the barrel surface. This current further induces greater quantities of air to enter the apertures 2&3 in the cooling jacket, the heated arnbient air being expelled through the vents 243 provided in the end plug 234. In addition, the cavitation created adjacent the gun muzzle along the projectile path, incident to tiring, still further induces the heated air from the jacket closure to flow outwardly through the end vents, and consequently urges even larger quantities of air to enter through side apertures 203. The above described cooling elfects, supplementing those accomplished by the normal heat transfer by conduction from the barrel to the jacket, and by the air otherwise entering the apertures 263, produces a semi-automatic and automatic gun which remains relatively cool despite continuous, extended tiring thereof.

To assemble the barrel, the breech portion 220 is inserted in the end of the cooling jacket, and manipulated with a slight rotative movement to enable the gas escape passageway 233 formed in the breech wall member 22), to clear the front sight and strap holder. Then, the vented end plug 23d is threaded in the jacket end region, which locates the breech wall and barrel in proper position, being maintained therein by the insertion of the locking screw 240.

The foregoing description is thought to have made apparent the operation of the actuator or bolt 26, iiring pin element 27, and spring 36 within the receiver 25. However, for purposes of completeness, it is noted that the gun will normally be carried, retained during inoperative times and picked up with the bolt handle or lever 54 in the safety slot 55. With the gun held in tiring position, a slight backward movement and partial clockwise rotation of the bolt will align the lever with the elongate slot 53. The bolt and pin will now be impelled a short distance forwardly by the recoil spring until stopped by the sear 184i. A pull on the trigger will release this main sear, allowing the spring to propel both pin and bolt toward the breech. Assuming the clip magazine, elsewhere herein referred to, to have been inserted into the tubular receiving sleeve, the top round in the clip will be forced by the clip spring into the space just back of the cartridge chamber. As the bolt moves forwardly, the feed guide machined into the bolt strips the cartridge from between the magazine lips and thrusts it into the tiring chamber. Instantaneously, the spring extractor claw 61 snaps over the head of the cartridge case, and the point 94 of the firing pin protruding through the bolt face 6) strikes the primer and lires the cartridge.

The gases generated in the cartridge case push the bullet down the barrel, and at the same time the reaction pushes the cartridge case itself back against the face 60 of the bolt. As the bullet is very light in comparison to the weight of the parts (pin and bolt) which must be moved back, and to the resistance of the recoil spring which must be compressed, the cartridge chamber 221 is delayed in opening fully, long enough to allow the dangerous gas pressure to drop.

After the cartridge is tired, the bolt and pin are moved rearwardly solely by the reaction of the case against the bolt face 60 until the case actually clears the cartridge chamber 221. At this instant the gas pressure has already dropped, as noted above, to a value such that it is no longer of dangerous magnitude, but there is sufcient gas pressure remaining to cause explosion gas to move quickly rearwardly from chamber 221. Almost at the same time as the case clears chamber 221 to release the gas, the case strikes ejector 223 and is thrown out the right side of the gun. With the case removed from the bolt face 60, the gas passage between the pin 27 and bolt 26 is opened.

According to this invention, a portion of the rearwardly moving gas in the receiver is directed back behind the bolt 26 to the por-tion of the receiver chamber 25 occupied by the recoil spring 3d. The open rear end of the tubular portion of tiring pin 27 communicates with the rear end of the receiver chamber to assure that there will be suflcient space in the rear portion of the receiver to accommodate the gases even when the bolt 26 and the pin 27 are at their rearmost positions. The gas in this space will assist the spring 30 in stopping the rearward movement of the bolt and in driving the bolt forwardly.

As the tiring pin 27 moves rearwardly, the gas in the chamber of tubular portion 85 and the gas in the remaining space at the rear end of the receiver chamber is compressed. lt will be noted that the center boss 41 of catch part 35 will intert the opening of tubular member 85, and will move into the gas chamber as the pin 27 moves to its rearwardmost position, hence serving to compress the gas trapped therein to an even greater degree. Of course, the boss 4l does not and need not completely close the opening to chamber S5, but is of sulicient diameter to cause the described compressive effect. The receiver, although open along the side to accommodate the bolt handle, is closed suiciently for this effect. This noted compressive effect on the gas in this space at the rear of the receiver chamber acts to decelerate the rearward motion of the tiring pin 27 and bolt 2d, and subsequently acts to urge the bolt and pin forwardly.

There are three paths the gas may take in order to iind its way into the chamber of tubular portion 85. First, the gas may follow the pin 27 rearwardly through the passage provided by the clearance between the pin 27 and the bolt 26, the gas acting on surfaces S7, 91 and 93 to move the pin slightly rearward relative to the bolt. The clearance between pin 27 and bolt 26 is shown in an exaggerated form in Fig. l0. The second path the gas may take is along channels 70 and 71, through passage 72 and thence into contact with the surfaces of 37 and 91. The gases from the rst and second paths meet at this juncture, and pass rearwardly between the tubular portion 35 of tiring pin 27 and the bolt 26, as permitted by sufficient clearance, to impinge on collar 95. A third path the gas may take is along groove 71, thence proceeding over the ridge 73 into the recess 74,

1.1 thence into groove 75 and through slot 77, and thence through recess 76 into impingement with collar 95.

After the gases from the three paths leave collar 95, the combined gases move rearwardly between the external part of tubular portion '85 and the receiver chamber into the space at the rear of the receiver chamber, this space including the chamber in tubular portion 85. It will be apparent that the major portion of such gas moves along the completely closed portions of the receiver chamber, such as at the top, the bottom and along lthe side opposite to that having the bolt handle-receiving slot 53. Only a very minor and insignciant portion of these gases moving along the described paths is released through -the openings in the receiver. 1t is apparent that the greater mass of pin 27 and of bolt 26 causes a relatively slower rearward movement of these parts than the rearward movement of the gas under pressure, hence the gas moves quickly to the rear portion of the receiver chamber and into the chamber of tubular portion 8S of pin 27, where lit is compressed in the manner previously described to assist in stopping the rearward motion of the pin and bolt.

It will be noted that in each of these paths, the tiring pin 27 acts as a valve in that the pin 27 must be moved rearwardly with respect to the bolt 26 so that the gas may pass along the paths into chamber 85. The so-called valve seats are represented in the rst path by frusto-conical surfaces 87, 91 and 93; in the second path by frusto-conical surfaces 87 and 91; and in the third path by the shoulder face 96 of bolt 26 and the collar 95. As the firing pin is moved rearwardly with respect to the bolt 26, these valve seats are open and permit the passage of gas to chamberSS. When the tiring pin 27 is then restored to its forwardmost position in the bolt, these valve seats are closed and the gas is trapped in the chamber of pin portion 85, and in the remaining space at the rear of the receiver behind the bolt.

The release of this trapped gas is realized during forward actuation of the pin 27 and bolt 26, the gas pressure being reduced and the gas merely passing through the openings in the receiver.

Thus, the explosive gases serve to cushion the deceleration of the bolt in its forward motion, to urge the bolt rearwardly, to assist the recoil spring in stopping the rearward motion, and to assist the spring in urging the bolt forwardly. This novel utilization of the gases in a gun of this type permits automatic operation at high speeds and reduces recoil.

The extreme simplicity of construction and arrangement of the firing assembly renders it particularly adaptable for quick and easy disassembly. As is best illustrated in Fig. 9, the rear catch elements are disengaged by pressing inwardly upon the slidable catch portion 36, which allows the tubular receiver structure to be pivoted about the screw 163. Then the breech cap 31 may be given a fractional part of a turn, and removed along with the spring, the rear end of which is secured thereto. Upon release of the sear and uri-ending the rifle, the bolt and firing pin assembly will fall rearwardly by gravity out of the receiver. New obviously, re-assembly is the reverse of these steps.

Although the invention has been described by making detailed reference to a single preferred embodiment, such detail is to be understood in an instructive, rather than in any restrictive sense, many variants being possible within the scope of the claims hereunto appended.

I claim as my invention:

1. In an automatic lire arm .of the blow back type, a barrel, a generally closed receiver aligned with the rear end of said barrel, a freely slidable bolt in said receiver having a longitudinal bore therethrough and being of such external shape as to form a longitudinal gas passageway along its external surface, a iiring pin slidable in the bore of said bolt, and a spring in the rear portion of said receiver bearing against said ring pin, said tiring pin including a rst valve portion rearwardly of its forward end and said bolt having a seat for such valve portion, the clearance between the firing pin and the portion of the bore in the bolt which is forwardly of said valve portion being sufficient to allow the passage of explosion gases rearwardly along said bore to said valve portion to move same away from its seat, said firing pin including a second valve portion rearwardly of said rst valve portion and said bolt having a transverse bore extending from said external passageway to said longitudinal bore in the vicinity of said second Valve portion to direct explosion gases onto said second Valve portion, whereby said explosion gases move said ring pin rearwardly relative to said bolt to allow the passage of gases to the portion of the receiver rearwardly of said bolt.

2. In an automatic re arm of the blow back type, a barrel, a generally closed receiver aligned with the rear end of said barrel, a freely slidable bolt in said receiver having a longitudinal bore therethrough and being of such external shape as to form a longitudinal gas passageway along the entire length of its external surface, a ring pin slidable in the bore of said bolt, and a spring in the rear portion of said receiver bearing against said firing pin, said firing pin including a first valve portion rearwardly of its forward end and said bolt having a seat for such valve portion, the clearance between the firing pin Vand that portion of the bore in the bolt which is forwardly of said Valve portion being suicient to allow the passage of explosion gases rearwardly along said bore to said valve portion to move same away from its seat, said firing pin including a second valve portion rearwardly of said rst valve portion and said bolt having a valve seat therefor at the rear end of said external passageway so that explosion gases are directed. onto said second valve portion, whereby said explosion gases move said tiring pin rearwardly relative to said bolt to allow the passage of gases to the portion of the receiver rearwardly of said bolt.

i References Cited in the le of this patent UNITED STATES PATENTS 357,170 Bjerkness Feb. 8, 1887 709,882 De Knight Sept. 30, 1902 877,657 Mason Jan. 28, 1908 908,294 Marga Dec. 29, 1908 1,020,596v Brauning Mar. 19, 1912 1,637,235 Norman July 26, 1927 1,786,207 Hudson Dec. 23, 1930 1,993,887 -Kewish Mar. 12, 1935 2,049,776 Hyde Aug. 4, 1936 2,251,304 Summerbell Aug. 5, 1941 2,353,601 Tisdale July 11, 1944 2,401,616 Clarke .Tune 4, 1946 2,423,109 Monnet July 1, 1947 2,425,684 Patchett Aug. 12, 1947 2,426,563 Patchett Aug. 26, 1947 2,457,835 Schiff Ian. 4, 1949 2,464,409 Mossberg Mar. 15, 1949 2,467,372 Permentier Apr. 19, 1949 2,492,815 Robinson Dec. 27, 1949 2,537,443 `Cerrella Ian. 9, 1951 FOREIGN PATENTS 3,565 Switzerland May 5, 1891 96,102 `Germany Feb. 12, 1898 343,572 Germany Nov. 4, 1921 453,658 Germany Dec. 15, 1927 221,036 Switzerland Aug. l, 1942 581,820 Great Britain Oct. 25, 1946 923,516 France July 9. 1947 

